It is widely known that electronic parts such as LSI, IC chips, etc., generate heat in use and thus, the performance thereof lowers owing to the heat generation. In order to solve this problem, a variety of heat dissipation techniques have been employed. One of ordinary methods includes placing a cooling member in the vicinity of a heat generation unit and bringing them in intimate contact with each other thereby dissipating heat by efficient removal of heat through the cooling member. In this connection, however, if there is a space between the heat generation member and the cooling member, thermal conduction does not proceed smoothly because of the presence of air, which is poor in thermal conductivity, so that the temperature of the heat generation member does not decrease satisfactorily. To prevent this, there have been conventionally used, for the purpose of preventing the presence of air, heat dissipating materials, heat-dissipating sheets or heat dissipating greases, which are good at thermal conductivity and are able to follow a surface profile of member (Japanese Patent Nos. 2938428, 2938429 and 3952184: Patent Documents 1-3).
Among heat dissipating greases, some greases are imparted with a bonding performance so as to cause a semiconductor chip and a heat spreader to be strongly bonded together. However, if there is no grease intervention between the semiconductor chip and the heat spreader, a satisfactory heat dissipation performance is not obtainable to considerably lower the performance, so that it is important to strongly bond the semiconductor chip and the heat spreader. Although these materials are high in bonding force, it has been frequently experienced that the hardness of the material increases through aging at high temperatures during use. The elongation of material lowers associated with the increased hardness, with the possibility that the strain of the chip caused by the thermal history of heat generation/cooling may not be followed, resulting in detachment or, in the worst case, leading to breakage of the chip.